The present disclosure relates generally to optical systems for distributing light from a light source and more particularly to an optical system for redirecting the light output of an LED into a vertically collimated, wide angle beam.
Commercially available LED's have characteristic spatial radiation patterns with respect to an optical axis which passes through the light emitting die. A common characteristic of all of LED radiation patterns is that light is emitted from one side of a plane containing the light emitting die in a pattern surrounding the LED optical axis, which is perpendicular to the plane. Light generated by an LED is radiated within a hemisphere centered on the optical axis. The distribution of light radiation within this hemisphere is determined by the shape and optical properties of the lens (if any) covering the light emitting die of the LED. Thus, LED's can be described as “directional” light sources, since all of the light they generate is emitted from one side of the device.
When designing light sources for a particular purpose, it is important to maximize efficiency by ensuring that substantially all of the generated light is arranged in a pattern or field of illumination dictated by the end use of the device into which the light source is incorporated.
The use of LED's in warning and signaling lights is well known. Older models of LED's produced limited quantities of light over a relatively narrow viewing angle centered on an optical axis of the LED. These LED's were typically massed in compact arrays to fill the given illuminated area and provide the necessary light output. More recently developed, high output LED's produce significantly greater luminous flux per component; permitting fewer LED's to produce the luminous flux required for many warning and signaling applications. It is known to arrange a small number of high-output LED's in a light fixture and provide each high-output LED with an internally reflecting collimating lens. The collimating lens organizes light from the LED into a collimated beam centered on the LED optical axis. Such an arrangement typically does not fill the light fixture, resulting in an undesirable appearance consisting of bright spots arranged against an unlit background. Light-spreading optical features on the outside lens/cover are sometimes employed to improve the appearance of the light fixture. It is also known to create wide angle light emission patterns by modifying the placement of the LEDs relative to the surface on which the light fixture is mounted. Angling or spacing the LEDs relative to a vertical surface can spread the light to be visible from a wide range of vantage points.
This application will discuss optical arrangements for modifying the emitted trajectory of light from an LED with respect to a reference line or plane. For purposes of this application, “collimated” means “re-directed into a trajectory substantially parallel with a reference line or plane.” Substantially parallel refers to a trajectory within 5° of parallel with the reference line or plane. When discussing collimation of light with respect to a plane, it will be understood that the component of the emitted trajectory divergent from the reference plane is modified to bring the divergent component of the trajectory within 5° of parallel with the reference plane, while the component of emitted trajectory parallel with the reference plane is not modified. For LEDs mounted to a vertical surface, light is emitted in a hemispherical pattern centered on the optical axes of the LEDs, which are perpendicular to the vertical surface, i.e., the optical axis of each of the LEDs is horizontal. If the LEDs are mounted in a row, the optical axes are included in the same horizontal plane, which is typically the horizontal reference plane. In this situation, “vertically collimated” means that light which would diverge upwardly or downwardly from the horizontal reference plane (containing the LED optical axes) is re-directed into a direction substantially parallel to the horizontal plane. Assuming no other obstruction or change of direction, vertically collimated light from each LED will be dispersed across an arc of approximately 180° in a horizontal direction. The light of adjacent LEDs overlaps to create a horizontal beam having a peak intensity many times the peak intensity of any one of the LEDs.
There is a need in the art for an optical element that redirects the light emitted from an LED into a vertically collimated, horizontally dispersed beam of light. There is a need to accomplish this light dispersion pattern while both filling the light fixture and mounting the light sources in a plane parallel to the mounting surface.